一.javascript 的函数定义方式：
方式1.
function square(x) {
return x*x;
}方式2.
var square = function(x) { return x*x; }
方式3.
var square = new Function("x", "return x*x;");//not often useful
二.Object
1.创建对象：
方式一.
var point= new Object();
point.x=2.3;
point.y=-1.2;
方式二.
var point = { x:2.3, y:-1.2 };2.When a non-null object is used in a Boolean context, it converts to true.
三.Array
1.JavaScript does not support multidimensional arrays.
2.When a variable holds the value null, you know that it does not contain a valid object, array, number, string, or boolean value.
3.undefined is returned when you use either a variable that has been declared but never had a value assigned to it or an object property that does not exist.
4.When the undefined value is used in a Boolean context, it converts to false. When used in a numeric context, it converts to NaN. And when used in a string context, it converts to "undefined"
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